J÷kulhlaup on Skei­arßrsandur from the GrÝmsv÷tn caldera

7th. of November 1996

Jokulhlaup started on the morning of November the 5th. quite abruptly.
The growth was fast and many icebergs were floating in the flood water
from the glacier reaching all the way to the sea. Grimsvotn tremour started at
21:30 on Monday 4th Nov, the jokulhlaup came out of the glacier 11 hrs
later. Distance is about 50 km from Grimsvotn to the Skeidararsandur.
The discharge growth was more sudden than was ever expected to be possible.
While all was quiet at 0800 the flood had increase its discharge 80-100
times in less than 2 hours.

Following river outlets were flooded:

N˙psvotn flooding starts around 1720 on 5th of Nov.Gigja, bridge fell at 13:00
Saeluhusakvisl lot of water flowed over the bridge
Skeidara strong current flow, bridge damaged

The estimated peak-flow was around 45.000 m3/s, that is about
10.000 to 15.000 m3/s higher than in the jokulhlaups of 1934 and
1938. Flood peak was reached at about 2300 hrs.
The flood has been decreasing rapidly since 2300 hrs on 5th of Nov.
The flood channel from Grimsvotn caldera can be clearly seen. It forms a
depression like structure on the surface of the glacier dotted with several
holes. It is estimated that the Grimsvotn lake has been totally emptied, since
the glacier seal has been destroyed due to melting of the water. This has never
occurred in Grimsvotn before. Such high melting can only be associated with
lake water temperature greater or equal to 10 deg. celsius.

It is now clear that the total damage are about 10-15 milj. US$,
these are the main constructions that were hit:

A small eruption started in Bardarbunga around 1300 hrs on 6th of Nov.
The eruption lasted for about 20 to 30 min. According to seismograms at the
Meteological office, the eruption was initiated by some intrusive activity.
The intrusive activity is based on recorded eruption tremor picked up by
on of the seismometers. Eruption column reached about 4 km in to the air.
Relation between pressure decrease due to the flooding have been suggested
as the main cause of the eruption.